As human knowledge has advanced, medical treatment has become progressively sophisticated. For example, it has become increasingly apparent to medical technicians that a patient has to receive intravenous fluid in precise amounts at preselected rates over extended periods of time. If the patient receives the fluid at a reduced rate, his ability to recover is impeded. However, if the patient receives fluid at a rate greater than the preselected value, he can often become poisoned by the chemicals in the fluid.
Systems have been provided in recent years for introducing controlled amounts of fluid to a patient at a preselected rate. For example, such a system is disclosed and claimed in U.S. Pat. No. 3,985,133 issued to Jon J. Jenkins et al on Oct. 12, 1976 for an "IV Pump" and assigned of record to the assignee of record of this application. A cassette is included in such a system. The cassette is provided with a chamber having a substantially constant cross section and is also provided with a plunger reciprocable in opposite directions in the chamber. The displacement and the rate of displacement of the plunger are precisely controlled by the system to provide for the introduction of the fluid to the patient at the preselected rate.
In the system disclosed and claimed in U.S. Pat. No. 3,985,133, the plunger has been provided with a pair of spaced lands and with a recess between the lands. Lubricating fluid has been provided between the recesses to lubricate the plunger as the plunger has been reciprocated. By lubricating the plunger, a continued and efficient reciprocatory movement of the plunger has been assured in most instances. However, the recess has occasionally become dry after some reciprocatory movement of the plunger. This has sometimes caused the plunger to become stuck in the chamber. The sticking has been aggravated by an expansion of the lands as a result of a generation of heat as the lands have moved through the chamber without any lubrication. This has caused the pump to become occluded and has prevented intravenous fluid from being transferred properly to a patient.